Green plants undergo photosynthesis to produce oxygen. In the process, water is splitted through photolysis and this results in production of two hydrogen atoms and one oxygen atoms. The oxygen is released, and hydrogen combined with carbon dioxide to form carbohydrate.
My idea is to trap the hydrogen before it is used up and funnel it to a storage tank, which then can be burnt to generate electricity. Theoretically, this could be done but then tiny nanoscopic devices will need to be integrated into the photosynthetic cells itself. The cells will then be supported by external nutrient agar so that it won't die by lack of food. With advances in biotechnology now, its not possible to genetically create a living cell with modified chloroplasts structure so that it produces more hydrogen when exposed to light.
The downside is that the green cells won't photosynthesise anymore since carbon dioxide isn't used. But then again if advances in biotechnology makes it possible to modify the chloroplasts structure further, then the green cells will be perpetually growing and self-sustaining. The only resource needed is oxygen, which is a by product of photosynthesis itself, water, which we have in plenty, and carbon dioxide, which we have so much that we don't know what to do with it.
The green cells then only needs to be put outside in direct sunlight. These green panels sort of work like solar panels, with the tubes connected on a molecular level to channel trapped hydrogen to a integrated power generating station. Or they could be used like fuel cells now, with the green panels on roofs of cars and a mini combustion engine that uses hydrogen as engines. Or they could be put up on roofs of recharging stations when electric cars are used in the future. Possibilities are endless.
Of course, for this to even happen, we need advanced knowledge in nanotechnology and biotechnology.
I dunno if this idea even makes sense or not. Just an idea.

